Requires ferrodoxin. Acts on cholesterol, cholest-5-en-3beta,7alpha-diol, 7alpha-hydroxycholest-4-en-3-one, 5beta-cholestane-3alpha,7alpha-diol as well as 5beta-cholestane-3alpha,7alpha,12alpha-triol. With cholesterol as well as 26-hydroxycholesterol, 24-hydroxy- and 25-hydroxycholesterol are also formed. With prolonged treatment, 26-hydroxycholesterol is converted into the corresponding 27-aldehyde and 27-oic acid.